The present invention relates to polymeric pyrrolidinium methane sulfonates which are viscosifiers, e.g., for use in enhanced oil recovery fluids and for use in drilling fluids. The invention further relates to methods for making these sulfonates.
In the recovery of oil from oil-bearing reservoirs, it usually is possible to recover only minor portions of the original oil in place by the so-called primary recovery methods which utilize only the natural forces present in the reservoir. Thus a variety of supplemental recovery techniques have been employed in order to increase the recovery of oil from subterranean reservoirs. The most widely used supplemental recovery technique is waterflooding which involves the injection of water into an oil-bearing reservoir. As the water moves through the reservoir, it acts to displace oil therein to a production system composed of one or more wells through which the oil is recovered.
One difficulty often encountered in waterflooding operations is the relatively poor sweep efficiency of the aqueous displacing medium; that is, the injected displacing medium tends to channel through certain portions of the reservoir as it travels from the injection system to the production system and to bypass other portions. Such poor sweep efficiency or macroscopic displacement efficiency may be due to a number of factors such as differences in the mobilities of the injected displacing liquids and the displaced reservoir oil and permeability variations within the reservoir which encourage preferential flow through some portions of the reservoir at the expense of other portions.
Various techniques have been proposed in order to improve the sweep efficiency of the injected displacing medium and thus avoid premature breakthrough at one or more of the wells comprising the production system. The most widely used procedure involves the addition of thickening agents to the injected displacing medium in order to increase the viscosity thereof and thus decrease its mobility to a value equal to or less than the mobility of the displaced reservoir oil, resulting in a "mobility ratio" of oil to water which is less than or equal to one. Many polymeric thickening agents including both anionic and cationic polyelectrolytes have been proposed for use in such mobility control operations. Thus, U.S. Pat. No. 3,085,063 discloses waterflooding in which the water is thickened by the addition of polyvinyl aromatic sulfonates such as sulfonated polystyrene and copolymers of such vinyl aromatic sulfonates. Similarly, U.S. Pat. No. 3,984,333 discloses waterflooding involving the injection of an aqueous solution thickened by block copolymers in which the water-soluble blocks are sulfonated polyvinylarenes and the relatively water-insoluble blocks are polymerized alpha olefins and/or hydrogenated dienes such as polyisoprene and polybutadiene. Synthetic anionic polymers such as those disclosed in the patents discussed above, as well as the more widely used partially hydrolyzed polyacrylamides, suffer a number of disadvantages in actual operations. Where the injected water or the reservoir water contains significant quantities of dissolved inorganic salts, their viscosity yield is decreased materially. Also U.S. Pat. No. 3,969,592 discloses water-soluble polymers manufactured by treating an aqueous suspension of protein with selected enzymes.
Also U.S. Pat. No. 4,110,232 discloses a waterflooding process for producing oil wherein an aqueous solution of a copolymer formed of hydrophobic olefinic segments and cationic aromatic segments is injected into oil-containing subterranean formation, and U.S. Pat. No. 4,222,881 discloses a waterflood oil recovery process involving the use of an amphoteric polyelectrolyte as a thickening agent for mobility control comprising a copolymer of a quaternary vinyl pyridinium sulfonate-styrene block copolymers.
During the drilling of an oil well, a usually aqueous fluid is injected into the well through the drill pipe and recirculated to the surface in the annular area between the well-bore wall and the drill string. The functions of the drilling fluid include: lubrication of the drill bit, transportation of cuttings to the surface, overbalancing formation pressure to prevent an influx of oil, gas or water into the well, maintenance of hole stability until casings can be set, suspension of solids when the fluid is not being circulated, and minimizing fluid loss into and possible associated damage/instability to the formation through which drilling is taking place.
Proper overbalancing of formation pressure is obtained by establishing fluid density at the desired level usually via the addition of barite (greater than or equal to 95% barium sulfate). Transportation of cuttings and their suspension when the fluid is not circulating is related to the fluid viscosity and thixotropy which depend on solids content and/or use of a polymer. Filter loss control is obtained also by the use of clays and/or added polymers.
Fluid properties are constantly monitored during the drilling operations and tailored to accommodate the nature of the formation stratum being encountered at the time. When drilling reaches the producing formation special concern is exercised. Preferentially low solids content fluids are used to minimize possible productivity loss by solids plugging. Proper fluid density for overbalancing formation pressure may be obtained by using high salt concentration aqueous brines while viscosity and filter loss control may be obtained by polymer addition. Substantial future oil well drilling will be at depths between 15 and 30 thousand feet where temperatures encountered can be 350.degree. F. Temperatures such as these, coupled with the desire for low solids content and preferably no added solids, require brine tolerant and high temperature stable polymers for viscosity and filtration control. Conventionally employed polymers such as starch, carboxymethyl cellulose, and modified polyacrylates are not stable at the temperatures in question and some have severe brine tolerance limitations.